1. Field of the Invention
The present invention relates to a horizontal form-fill-seal packaging machine and a method of controlling the same, which permit a continuous packaging of articles having different length and supplied to the machine at random, by varying the package length with the length of each article to be packaged.
2. Description of the Prior Art
A conventional horizontal form-fill-seal packaging machine includes a film supply roll, a former, an article supply conveyor, a fin sealer, and an end sealer. A long thermoplastic film is continuously fed from the film supply roll to the former where the film is formed into a tubular configuration. The article supply conveyor feeds articles into the tubular film one after another. The fin sealer provides a seal in the longitudinal direction of the tubular film at its lapped side edges. The end sealer provides a seal in a crosswise direction of the tubular film on both sides of each article in the longitudinal direction, so that desired packages are formed in succession.
Such a conventional horizontal form-fill-seal packaging machine is disclosed in Japanese Patent Publication No. 51-34787 entitled "Packaging Machine" and Japanese Laid-Open Patent Publication No. 4-57708 entitled "Horizontal Form-Fill-Seal Packaging Machine".
In the "Packaging Machine" disclosed in Japanese Patent Publication No. 51-34787, in order to feed articles into a tubular film with the distance between two adjacent articles automatically adjusted, a first conveying mechanism and a second conveying mechanism are provided in an article feeding section. During the transmission of the articles from the first conveying mechanism to the second conveying mechanism, the articles are fed into the tubular film with the distance between the rear end of each article and the front end of the rearwardly positioned one is adjusted to coincide with a distance between two detectors. In addition, in order to seal the tubular film at a central position between two adjacent articles fed into the tubular film, a sensor is positioned just before an end sealer to detect the rear portion of each article which passes a position besides the sensor, so that the end sealer stopped in a predetermined rotational position is started for rotation. The tubular film is consequently sealed and cut in a position between two adjacent articles which are fed from a supply conveyor to the tubular film at constant intervals.
The "Horizontal Form-Fill-Seal Packaging Machine" disclosed in Japanese Laid-Open Patent Publication No. 4-57708 incorporates, as a supply conveyor for supplying articles to be packaged into a tubular film one after another, a belt-driven supply conveyor which is rotatably driven at a uniform speed. An article detection sensor is disposed on the conveyor to detect the articles for variably controlling the feeding speed of the film as well as the rotational speed of an end sealer, so that the film is fed by an amount in response to the length of each article and so that the crosswise sealing of the tubular film is performed in a central position between each two adjacent articles fed into the tubular film at constant intervals.
With the "Packaging Machine" disclosed in Japanese Patent Publication No. 51-34787, since the machine is repeatedly started and stopped by clutch and brake devices provided in the first and second conveying mechanisms and the end sealer, respectively, the machine involves a disadvantage that it is not suitable for a high-speed operation. Further, because of vibrations which may be produced when the machine is started or stopped, the articles are liable to be moved from their proper positions. Therefore, as disclosed in the description of the preferred embodiment of this publication, it is necessary to hold the articles by upper and lower belts during transportation, causing another problem such as lower productivity and higher manufacturing costs because of complex construction of the whole machine.
Additionally, with this packaging machine, the rotation of the end sealer is started when the rear portion of each article fed into the tubular film is detected by a photoelectric sensor. Therefore, if a film for packaging articles therein is not a transparent one, it is difficult to detect the articles and it is not possible to start rotation of the end sealer.
Further, since the starting of rotation of the end sealer depends only on the detection of the rear portion of each article by the sensor positioned just before the end sealer, no crosswise seal is made in a position forwardly of the article which has been fed at the first time, so that an improper packaging is caused.
On the other hand, with the "Horizontal Form-Fill-Seal Packaging Machine" disclosed in Japanese Laid-Open Patent Publication No. 4-57708, since the feeding speed is varied with change of the length of articles detected by the article detection sensor, the distance between two adjacent articles fed into the tubular film may be varied in response to an instantaneous change in the feeding speed, particularly during a high-speed operation. Further, such change in the film feeding speed may cause unstable lengthwise and crosswise seal of the film, so that the sealing operation cannot be properly performed.